Tohoku University, Institute of Development, Aging and Cancer, Sendai 980-8575, Japan.
J Neurophysiol. 2010 Dec;104(6):3388-412. doi: 10.1152/jn.00122.2010. Epub 2010 Sep 1.
Microelectrode arrays used to record local field potentials from the brain are being built with increasingly more spatial resolution, ranging from the initially developed laminar arrays to those with planar and three-dimensional (3D) formats. In parallel with such development in recording techniques, current source density (CSD) analyses have recently been expanded up to the continuous-3D form. Unfortunately, the effect of the conductivity profile on the CSD analysis performed with contemporary microelectrode arrays has not yet been evaluated and most of the studies assumed it was homogeneous and isotropic. In this study, we measured the conductivity profile in the somatosensory barrel cortex of Wistar rats. To that end, we combined multisite electrophysiological data recorded with a homemade assembly of silicon-based probes and a nonlinear least-squares algorithm that implicitly assumed that the cerebral cortex of rodents could be locally approximated as a layered anisotropic spherical volume conductor. The eccentricity of the six cortical layers in the somatosensory barrel cortex was evaluated from postmortem histological images. We provided evidence for the local spherical character of the entire barrels field, with concentric cortical layers. We found significant laminar dependencies in the conductivity values with radial/tangential anisotropies. These results were in agreement with the layer-dependent orientations of myelinated axons, but hardly related to densities of cells. Finally, we demonstrated through simulations that ignoring the real conductivity profile in the somatosensory barrel cortex of rats caused considerable errors in the CSD reconstruction, with pronounced effects on the continuous-3D form and charge-unbalanced CSD. We concluded that the conductivity profile must be included in future developments of CSD analysis, especially for rodents.
用于记录大脑局部场电位的微电极阵列的空间分辨率越来越高，从最初开发的层状阵列到平面和三维 (3D) 格式。随着记录技术的发展，电流源密度 (CSD) 分析最近已扩展到连续 3D 形式。不幸的是，对于当代微电极阵列进行的 CSD 分析，尚未评估电导率分布的影响，并且大多数研究都假设它是均匀和各向同性的。在这项研究中，我们测量了 Wistar 大鼠体感皮层的电导率分布。为此，我们结合了使用自制硅基探针组件记录的多部位电生理数据和非线性最小二乘算法，该算法隐含地假设啮齿动物的大脑皮层可以局部近似为分层各向异性的球形体积导体。从死后组织学图像评估了体感桶状皮层的六个皮层层的偏心度。我们提供了整个桶状场具有同心皮层层的局部球形特征的证据。我们发现了与径向/切向各向异性相关的明显的分层依赖性的电导率值。这些结果与有髓轴突的分层依赖性取向一致，但与细胞密度几乎没有关系。最后，我们通过模拟证明，在大鼠体感皮层中忽略实际电导率分布会导致 CSD 重建中出现相当大的误差，尤其是在连续 3D 形式和电荷不平衡 CSD 方面。我们得出结论，在未来的 CSD 分析开发中，必须包括电导率分布，特别是对于啮齿动物。
